In psychological studies, random assignment refers to the use of procedures that guarantee that each participant has the same probability of assignment or choice in the study groups.
It is necessary to take into account that random assignment and random selection are different, since the first refers to the distribution of participants in random and balanced ways in experimental groups and the second refers to the selection of individuals capable of representing certain characteristics of a population
Answer
The experimental methodological aspect that Buster can point out to refute that criticism is the random assignment, whereby study participants are randomly assigned to different groups.